CD21 Cell Count in Blood
This test measures the number of CD21-positive cells in your blood, which are a type of immune system cell involved in helping the body fight infections and respond to antigens.
["CD21 cells play a key role in immune function and may be checked if you have suspected immune disorders."]
Key facts at a glance
- LOINC
- 8120-8
- Short code
- CD21
- Synonyms
- CD21 Cells NFr Bld
- Category
- chemistry
- Sample
- whole-blood
- Container
- EDTA (lavender-top) vacutainer tube for flow cytometry immunophenotyping; sodium heparin (green-top) tube is an acceptable alternative
- Units
- N/A
- Ref low
- 5
- Ref high
- 15
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Flow cytometry using fluorescently labeled monoclonal antibodies against CD21 surface marker; results expressed as percentage of total lymphocytes and absolute count (cells/μL)
- CPT
- 86355
- SNOMED
- 116852008
- Specimen volume
- 3-5 mL whole blood for adults; minimum 1 mL for pediatric patients; sufficient volume required to perform viability assessment and lymphocyte gating
- Stability
- Specimen should be processed within 24-30 hours of collection when stored at room temperature (18-25°C); do not refrigerate or freeze as this may compromise cell viability and surface antigen expression
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 24–72 hours
- Order
- routine
What Does This Test Measure?
CD21 cells are a subset of B lymphocytes (a type of white blood cell) that help regulate the immune response. This test counts the cells expressing CD21, a protein found on their surface. The result helps assess immune function, particularly in conditions affecting B cells.
Why Might This Test Be Ordered?
Your healthcare provider may order this test if you have symptoms like frequent infections, autoimmune diseases, or if you’re being evaluated for conditions such as Wiskott-Aldrich syndrome, common variable immunodeficiency, or other immune deficiencies.
Sample and Testing Process
A blood sample is drawn from a vein, usually in your arm. The sample is processed to count CD21-positive cells using specialized laboratory techniques, such as flow cytometry.
What to Expect Before or After Testing
No special preparation is needed for this test. You may experience mild discomfort or bruising at the injection site, but this usually resolves quickly. Results may take a few days to a week to be reported.
Reference range
Reference ranges for CD21+ B-lymphocytes in peripheral blood typically range from 5-15% of total lymphocytes and approximately 100-300 cells/μL in absolute count; values vary by laboratory and should be interpreted using the performing lab's reference intervalN/A
No special preparation required; patients should inform the laboratory of any recent corticosteroid, immunosuppressive, or chemotherapy use that may affect lymphocyte subset counts
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Low CD21 cell counts may indicate immune deficiencies or disorders affecting B cell development and function. High counts could be seen in certain immune responses or conditions like monoclonal gammopathy. Always discuss results with your healthcare provider, as they will interpret them in the context of your overall health and symptoms.
Short name
CD21 Cells
Frequently asked questions
How is this test different from other B cell tests?
Can diet or medications affect this test?
What if my results are outside the expected range?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy